Closed cycle paper sheet production

ABSTRACT

Construction paper sheets are produced from groundwood stock and other fibrous stocks without undesired sludge accumulation and without undesired discharge of high BOD waste water streams to the environment. The sludge formed upon separation of colloidal material from said waste water streams is coated on the individual strands of wood fiber and, in this form, is recycled to the stock milling zone as a wood stock ingredient of the furnish from which the sheet, e.g., roofing felt, is fabricated. Sludge formation is facilitated by the addition of clay particles to the waste water stream for adsorption of colloidal material therefrom. A flocculent can also be employed to enhance the separation of said clay containing adsorbed material from said waste water stream. The effluent waste stream containing dissolved solids is recycled to said milling zone as make-up water. The sheet fabricated in such closed-cycle operations has properties comparable to those of sheets not having said sludge incorporated therein.

United States Patent 11 1 Frost, III.

[451 May 20, 1975 1 CLOSED CYCLE PAPER SHEET PRODUCTION [75] Inventor:Arthur W. Frost, III., Lansdowne,

[52] US. Cl. 162/190; 162/147; 162/D1G. 9 [51] Int. Cl. D21f l/66 [58]Field of Search 162/189, 190, 158, 182, 162/150, 142, 147, 168, DIG. 9;210/45, 52, 54

[56] References Cited UNITED STATES PATENTS 3,019,157 1/1962 Reynolds eta1. 162/168 3,130,167 4/1964 Green 210/52 X 3,262,877 7/1966 Le Compte,Jr.... 162/190 X 3,276,998 10/1966 Green 210/52 3,364,101 1/1968 Eek162/189 X 3,450,680 6/1969 .lursich et al.... 162/168 X 3,576,710 4/1971Mader et a1. 162/190 X 3,769,116 10/1973 Champeau 162/DIG. 9

FOREIGN PATENTS OR APPLICATIONS 1,275,042 5/1972 United Kingdom l62/DIG.9 273,650 1970 U.S.S.R 162/147 163,501 1955 Australia 162/168 OTHERPUBLICATIONS Abstract Bul. Institute of Paper Chem., Vol. 41, No. 3(9-1970), Abstract No. 2261, Dvorak.

Brown, Use of White Water in Manufacture of Groundwood Pulp and Effecton Freeness, Tappi, Tech. Assoc. Papers, Series VI, pp. 91-93.

Primary Examiner-S. Leon Bashore Assistant ExaminerA. DAndrea, Jr.

Attorney, Agent, or FirmWalter C. Kehm; Joshua J. Ward [57] ABSTRACTConstruction paper sheets are produced from groundwood stock and otherfibrous stocks without undesired sludge accumulation and withoutundesired discharge of high BOD waste water streams to the environment.The sludge formed upon separation of colloidal material from said wastewater streams is coated on the individual strands of wood fiber and, inthis form, is recycled to the stock milling zone as a wood stockingredient of the furnish from which the sheet, e.g., roofing felt, isfabricated. Sludge formation is facilitated by the addition of clayparticles to the waste water stream for adsorption of colloidal materialtherefrom. A flocculent can also be employed to enhance the separationof said clay containing adsorbed material from said waste water stream.The effluent waste stream containing dissolved solids is recycled tosaid milling zone as make-up water. The sheet fabricated in suchclosed-cycle operations has properties comparable to those of sheets nothaving said sludge incorporated therein.

26 Claims, No Drawings CLOSED CYCLE PAPER SHEET PRODUCTION BACKGROUND OFTHE INVENTION 1. FIELD OF THE INVENTION This invention relates to theproduction of paper sheets. More particularly, it relates to closedcycle construction paper sheet production with essentially zero effluentdischarge.

2. DESCTIPTION OF THE PRIOR ART In the production of paper sheets, ithas been common practice to blend fibrous stocks with water, togetherusually with other known non-fibrous ingredients, in a milling zone, toproduce an aqueous suspension from which a sheet of the desired paper isfabricated. The fibrous and non-fibrous materials blended together inwater suspension are generally collectively referred to as the furnish.The nature of the furnish will vary with the kind and grade of paperproduced and even with the individual practices of particular mills. Forconstruction paper applications, as for example in the production ofroofing felts, groundwood pulp produced by a mechanical pulping processis commonly employed in preference to pulps produced by chemicalprocesses, such as sulfite, soda and sulfate pulps. In such constructionpaper applications, the groundwood pulp may typically comprise abouttwothirds of the fibrous stock components of the furnish on a wet weightbasis, the remainder of the fibrous stock generally comprising paperstock and rag stock in varying amounts as is well known in the art.

The sheet of paper is fabricated from the aqueous suspension on a papermachine, such as a fourdrinier machine or a cylinder machine, bydewatering the stock and surface finishing the sheet produced. Thedewatering is accomplished in a manner that produces a sheet of uniformstructure and thickness through the application of natural drainage,induced drainage by partial vacuum, roll pressure and by heat. The waterthus removed from the fabrication zone, commonly referred to as vatspill water, will generally contain a variety of dissolved and suspendedmatter associated therewith. The vat spill is sometimes blended withother refuse waters, producing a so-called dirty white water stream.From this latter stream, particulate objects can be removed by cyclones,screening and the like, and suspended fibers are separated by suitablefilters and the like, generally for recycle to the milling zone as paperstock.

The thus-treated dirty white water stream having particulate objects andan appreciable portion of the suspended fiber removed therefromcomprises a so-called clean white water stream. On the order of about80% by weight of said clean white water stream is conventionallyrecycled to the wood defibrators in which the groundwood stock isproduced and to the hydrapulpers in which mixed paper stock isprocessed.

The remaining portion of the clean white water stream, i.e., commonly onthe order of about by weight thereof, may be passed through disc filtersor the like to further reduce the suspended fiber content thereof, therelatively clear filtrate or effluent aqueous stream having colloidalmaterial suspended therein, together with dissolved solids such aslignin derivatives and other residues of the pulping operation employinggroundwood stock.

The effluent aqueous stream has a relatively high biological oxygendemand, i.e., BOD, rendering it unacceptable from an environmentalviewpoint for discharge to rivers, lakes and tributary streams. Becauseof the growing awareness and concern relating to water pollutionresulting from the discharge of industrual wastes into water streams,various national and state water pollution control laws and regulationsare presently in effect or under serious consideration to minimize andcontrol water pollution resulting from the effluent'discharges of thepulp and paper industry and other industrial processing operations.

Efforts to avoid water pollution resulting from the indiscriminatedischarge of the effluent aqueous stream referred to above have includedthe separation of a sludge of colloidal solid wastes from said stream,by clarification and the like, together with various primary, secondaryand even tertiary systems of water treatment to acheive 90% or higherremoval of contaminants to meet the ever more restrictive BOD reductionstandards for permissible effluent aqueous discharge to receivingwaters. Such efforts impose, of course, a considerable economic burdenupon the overall pulp and paper production operation, however necessarysuch water pollution controls may be from an environmental viewpoint.Marginal operations may not be able to continue because of the economicinfeasibility of meeting operable water pollution control requirements.The economic impact of the highly desirable control standards is furtheraggravated by the necessity of additional operating expenditures forsludge storage and disposition. In continuous mill operations, thequantities of effluent aqueous waste streams and accumulated sludge thusrequiring treatment and/or disposal become such as to result in theexpenditure of very considerable sums for pollution control purposes ineven the most efficiently run operations.

In an effort to reduce such expenditures, the recycling of accumulatedsludge to the milling zone has been proposed in order to reduce theamount of sludge that must be transported to acceptable waste disposalfacilities. The incorporation of the sludge as one of the ingredients ofthe furnish was not generally satisfactory, however, since the presenceof the sludge tends to disrupt the orientation of the fibers during theproduction of the sheet, the properties of the sheet thereby sufferingto an unacceptable extent. The presence of said sludge particles betweenthe fibers was likewise found to adversely affect the drainagecharacteristics of the sheet being fabricated so as to disrupt theoperational efficiency of the fabrication operation as well as thequality of the resultant sheet.

In some instances, efforts to recycle the effluent aqueous stream to themilling zone have proved more successful than efforts to recycleaccumulated sludge thereto. There has been a tendency, however, toconcentrate more upon the improvement of BOD reduction techniquespermitting the discharge of all or substantial portions of said effluentaqueous streams to receiving waters as waste water steams of acceptablylow BOD content. The reluctance to pursue the recycle of the effluentaqueous stream is, at least in part, motivated by concerns relating tothe buildup of dissolved solids in the system and their effect on theproperties of the sheet being fabricated and upon the sludgeaccumulation and disposal operations that must, in any event, becontinued in operations of this type.

It is an object of the present invention, therefore, to provide animproved sheet fabrication operation.

It is another object of the invention to provide an improved sheetfabrication having enhanced water pollution control features.

It is another object of the invention to provide a sheet fabricationoperation in which the disposition of sludge is facilitated.

It is another object of the invention to provide a sheet fabricationoperation in which water pollution and sludge disposal are obviated.

It is another object of the invention to provide a construction papersheet produced with essentially zero effluent discharge from the overallsheet fabrication operation.

With these and other objects in mind, the invention is hereinafter setforth in detail, the novel features thereof being particularly pointedout in the appended claims.

SUMMARY OF THE INVENTION The sludge of solids separated from theeffluent aqueous stream resulting from the fabrication of constructionpaper sheets from a furnish containing groundwood and other fibrousstocks is coated on the individual strands of groundwood fibers that areto form the groundwood stock component of additional furnish employed incontinuous sheet fabrication operations. When recycled to the millingzone in this manner, the sludge does not disrupt the orientation of thefibrous material, with resultant adverse effect upon the properties ofthe sheet, as when the accumulated sludge is recycled directly to themilling zone. A cationic polyelectrolyte may be employed as a bondingagent to enhance the adherence of the sludge to the groundwood fibers.The effluent aqueous stream having dissolved solids therein that obtainsupon removal of the colloidal material therefrom is also recycled to themilling zone as make-up water. The accumulation of dissolved solidstherein is readily accommodated as all of the solids beyond thesaturation level of said effluent aqueous stream are accumulated in thesludge, resulting in a closed cycle operation with essentially zeroeffluent discharge. The effluent aqueous stream recycled to the millingzone is at an elevated temperature, thereby minimizing the overall heatrequirements of the system. The construction paper sheet obtainded withsaid closed cycle operation and essentially zero effluent discharge hasproperties and characteristics comparable to those of said sheetsfabricated without said effluent aqueous stream and said sludge recycle.

DETAILED DESCRIPTION OF THE INVENTION The present invention serves toobviate the environmental concern relating to the disposal of liquid andsolid waste materials in construction paper sheet production byproviding for the recycle of said waste materials to the sheetfabrication operation with essentially zero effluent discharge to waste.Such closed cycle operation is achieved, in the practice of theinvention, which producing construction paper sheets of comparablequality to those produced with effluent aqueous steam and sludge recyle.The invention thus represents a highly important advance in the pulp andpaper industry, providing a practical and economically attractiveprocess satisfying fully the environmental imperative of overcoming thewater pollution and sludge disposal problems associated withconventional sheet fabrication operations.

The present invention is applicable in the production of constructionpaper made from groundwood stock, but is not generally applicable forthe production of writing paper and other fine grade papers producedfrom fibrous stocks prepared by chemical pulping processes. While theinvention is thus advantageously suited for the production of variousgrades of roofing felt, including asphalt saturated paper, it willreadily be appreciated by those skilled in the art that a variety ofother sheets will fall within the scope of the term construction paperas used herein. Illustrative of such other sheets are so-calleddeadening felts, stuffing materials, table pads, combination box boardand the like. The present invention includes within its scope all suchgrades of construction paper produced with the waste sludge materialincorporated therein as herein provided by the coating thereof on thegroundwood stock component of the furnish from which the paper sheetsare produced.

As is well known in the art, the groundwood pulp process is mechanicalin character, and the use of groundwood stock in the production ofconstruction paper sheets contributes to the existence of a dirty whitewater stream having a variety of dissolved and suspended matter presenttherein, including various organic acids, lignin derivatives and thelike, as well as suspended fibers, particulate objects and generaldebris. Upon removal of particulate objects, debris, and an appreciableportion of the suspended fiber content, the resulting aqueous stream,referred to as a clean white water stream, is typically divided into twostreams, one comprising generally a major portion of said clean whitewater stream being commonly recycled to hydrapulpers and defibratorsused in the production of additonal quantities of fibrous stock asindicated above, the second stream comprising generally a minor portionof said clean white water stream, e.g., on the order of about 20%thereof by weight, being generally treated for the removal of additionalquantities of suspended fibers and colloidal waste materials collectedas sludge. In the practice of the present invention, the sludge isrecycled with groundwood stock for ultimate incorporation in the sheetbeing fabricated. The effluent aqueous stream having dissolved solidstherein, upon removal of said fibrous material and said sludge, islikewise recycled as make-up water, with the accumulation of solublesolids in excess of the dissolving capacity of said stream and of thedirty and clean white water streams resulting in said excess solidsbeing separated therefrom in the sludge. The fibers separated from saidaqueous streams, as indicated above, can likewise be recycled for reuseas a paper stock component'of the furnish of fibrous and non-fibrousmaterials that are blended together in aqueous suspension to ultimatelyproduce the construction paper sheet of the present invention.

Those skilled in the art will appreciate that the groundwood stock iscommonly blended with other fibrous materials, as well as withconventional nonfibrous ingredients, to produce the furnish referred toabove. Paper stock, including the recovered fibers originally suspendedin the dirty white water stream removed from the sheet fabricationoperation, are also commonly blended with said groundwood stock. Ragstock, as is known in-the art, comprises another common fibrousingredient of the furnish. In the production of roofing felt, forexample, about two-thirds by weight of the total fibrous stock, on a wetfiber basis, generally comprises wood stock, i.e., groundwood stock,with about one-third to about 40% by weight typically comprising paperstock, with the balance, typically less than by weight, comprising ragstock. It will be appreciated that the precise proportions of saidgroundwood stock, said paper stock and said rag stock, are not criticalfeatures of the invention and will vary in particular embodiments as aresult of varying mill requirements, paper specifications and the like.It should also be noted that, on a dry fiber weight basis, the amount ofwood stock employed will be about a half that employed on a wet basis.Those skilled in the art will appreciate that all of the wood stockcomponent of the furnish need not comprise groundwood stock although itwill be generally advantageous to thus employ groundwood as the onlywood stock in the construction paper applications of the presentinvention.

In the practice of the invention, it has been desirably determined thatall of the accumulated sludge can be recycled without adverse effectupon the properties of the sheet by the coating thereof on theindividual strands of groundwood fiber as herein provided. In continuoussheet fabrication operations, therefore, the typical groundwood stockcomponent of the fibrous portion of the furnish will be entirelyadequate in amount for the coating thereon of all of the accumulatedsludge. No groundwood requirements in excess of those pertaining toconventional operations are thus applicable in the practice of theprocess of the present invention. On the other hand, it is within thescope of the invention to coat the accumulated sludge on only a portionof the groundwood stock component of the furnish, with the remainder ofsaid groundwood being employed directly in the furnish without beingprecoated with sludge as herein provided.

As previously indicated, the invention includes within its scope theproduction of any construction paper sheet the specifications of whichdo not preclude the presence of the accumulated sludge therein. Thetypical proportions of fibrous components for roofing felts will not, ofcourse, necessarily apply with respect to other construction paperapplications. The relative proportion of wood stock i.e., groundwood,employed is again not a critical feature of the invention, it beingunderstood that a sufficient amount of groundwood stock will be employedso that all of the separated sludge can be coated upon the individualstrands of wood fiber, with essentially no excess sludge remaining thatnecessarily can not be processed with the wood fibers. The invention, ineffect, comprises a closed cycle operation with essentially zeroeffluent discharge in its preferred and entirely feasible operations.Those skilled in the art will appreciate, however, that any portion ofthe accumulated sludge can be recycled in accordance with the presentinvention, the remaining portion of the sludge being discarded to wasteas in conventional operations. Such limited sludge recycle operationsare not preferred, however, since the typical wood fiber component ofthe furnish is entirely capable of readily accommodating all of theaccumulated sludge without adverse effect on the properties-of thesheet, thus obviating the additional expense of sludge storage anddisposal.

In conventional construction paper operations and in the presentinvention, fibrous stocks, including groundwood stock, together withconventional non-fibrous ingredients, are blended together with water ina milling zone to produce an aqueous suspension of said stocks. In thisoperation, the resulting suspension is heated typically to on the orderof about l35-l40F as by the introduction of steam-heated wood stock tothe milling zone. The thus-blended stock is thereafter dewatered in asheet fabrication zone, e.g., a conventional paper making machine suchas a fourdrinier machine, in which a sheet of uniform structure andthickness is produced and thereafter surface finished in conventionalmanner. As previously indicated, dewatering is commonly achieved by acombination of natural drainage, induced drainage, roll pressure andheat. The waste water stream i.e,. that the vat spill water stream,removed from the fabrication zone is at an elevated temperature thatwill vary with the individual mill practice, but which will rangegenerally from about F to about 150F or more, typically on the order ofabout -140F. By the recycle of the effluent aqueous stream to themilling zone rather than its treatment and discharge to receivingwaters, the process of the invention achieves an appreciable savings inthe overall heat requirements of the milling and sheet fabricationoperations as noted below. As further in accordance with conventionaloperations, particulate objects and suspended fiber and other matter areremoved from the waste water stream by various commonly availableseparation devices, such as cyclones, screens, filters, etc., as is wellknown in the art. The resulting effluent aqueous stream at this pointgenerally known as a clean white water stream, has a very much reducedsuspended fiber content, together with dissolved and colloidal material.In conventional mill practice, as indicated above, a major portion ofsaid clean white water stream is commonly passed to hydrapulpers anddefibrators employed in the production of additional quantities offibrous stock. The remaining portion of said stream is commonly passedthrough disc filters or other suitable devices for removing essentiallyall of the remaining suspended fibers, the effluent aqueous stream thusresulting comprising an essentially clear filtrate having a minimalsuspended fiber content. The suspended fibers removed from the dirtywhite water stream and form the clean white water stream can, ifdesired, be recycled to the milling zone as a paper stock component ofthe furnish. The effluent aqueous stream will, of course, have dissolvedand colloidal material present therein, said stream having a relativelyhigh BOD loading. It is this stream that, in conventional operations, istreated so as generally to separate a sludge of colloidal mattertherefrom and to reduce its BOD loading, by primary, secondary and eventertiary methods, so as to meet applicable BOD reduction standards andregulations and thus permit the discharge of said treated aqueous streamto rivers and other receiving waters. In accordance with the presentinvention, on the other hand, said effluent aqueous stream need not betreated for such BOD reduction as it is recycled to the milling zone, asis the accumulated sludge in an essentially zero effluent dischargeoperation.

In the practice of the invention, colloidal material is separated fromthe effluent aqueous stream as a sludge of waste solids material, boththe sludge and the effluent aqueous stream having dissolved solidstherein being recycled to the milling zone. While the colloidal materialmay be separated from the effluent aqueous stream in any suitableseparation or clarification zone,

employing any suitable, commercially available cyclone or otherclarification equipment, it has been found generally advantageous todisperse bentonitic clay particles in the effluent aqueous stream havingdissolved and colloidal material present therein. The bentonitic clayparticles serve to adsorb the colloidal material form the effluentstream, thus facilitating the separation of the colloidal material fromthe effluent stream. It is further desirable, in those embodiments ofthe process of the invention in which clay particles are thus employedto adsorb colloidal material, to add a water-dispersible flocculent tothe effluent stream subsequent to the dispersing of clay particlestherein. The flocculent serves to further enhance the separation of thesludge material from the aqueous stream by flocculating the clayparticles having colloidal material adsorbed thereon. In suchembodiments, of course, the sludge recycled to the milling zone willcomprise said colloidal material adsorbed on the clay particlesflocculated by said flocculent, as opposed to the sludge settled orseparated from the aqueous stream by other techniques or methods not soemploying clay particles and a flocculent.

The bentonitic clay is conveniently employed as an about 1% to about 4%,e.g., about 2%, by weight slurry in fresh water. Illustrative of thecommercially available clays that can be employed are KWK VolclayBentonite, a granular product of American Colloid Company, withanaverage particle size of between 20 and 70 mesh, U.S. Screen, having amontmorillonite content of at least about 90% by weight, and COAGU-LOlD-20l montmorillonite clay, of Baroid Division N L Industries, lnc.,with a screen analysis of about 90% through a 200 mesh screen. While itwill be appreciated that the amount of clay particles employed willdepend upon a number of factors, such as the particular nature of thecolloidal material to be adsorbed, the amount of said material to beadsorbed, the desired clarification rate, and the like, it has beenfound convenient to employ from about 200 ppm to about 250 ppm by weightbased on the total weight of the aqueous stream being treated. It willbe understood, however, that dosage levels outside this range mayreadily be employed in the desired separation of a sludge of wastesolids material form the effluent aqueous stream.

As a flocculent or secondary coagulant, any suitable, commerciallyavailable cationic flocculent may be employed. Suchflocculents arecommonly very high molecular weight materials, such as flocculentshaving molecular weights of on the order of about 2 t 6 million or more.illustrative examples of suitable, commercially available flocculentsthat may be employed are Betz Polymer 1260, a cationic, extremely highmolecular weight, organic copolymer of acrylamide, and Magnifloc 560-Cof American Cyanamid Company, likewise a very high molecular weightcationic polyelectrolyte solid. The flocculent is generally added to theaqueous stream as a slurry in fresh water at a concentration of about0.05% to about 0.5%, conveniently about 0.1%, by weight. While it willbe appreciated that the amount of flocculent employed will also dependupon a number of factors, such as those indicated above with respect tothe addition of clay, quantities within the range of from about 7 toabout ppm by weight based on the total weight of said effluent aqueousstream being treated may be employed, it being understood that dosagelevels outside this range may be employed in partic- As indicated above,varios clarification systems can be employed in the practice of theinvention. Thus, a multiple batch tank clarifier may be employed inwhich the effluent aqueous stream passes into one tak for treatment, andflows to other tanks for sludge settling ,and the like and for ultimatetransport back to the milling zone as make-up water. In otherembodiments, continuous clarifier units may be employed, as for exampleso-called upflow clarifiers in which the stream being treated is passeddownwardly and upwardly through a clarifier device with appropriateprovisions made for the addition of clay particles and subsequently theflocculent material thereto if desired. While the time period desirablebetween the addition of clay particles and of the flocculent will varydepending upon the overall circumstances of any given application, suchtime period will generally be at least a few minutes, with a period offrom about 2 to about 5 minutes being particularly advantageous in manyapplications.

The effluent aqueous stream having dissolved solids therein, but havingcolloidal material removed therefrom, is returned to the milling zone asmake-up water at a pH on the acid side, typically on the order of fromabout 4 to about 5.5, e.g., about 4.2-4.5, in the absence of theaddition of a suitable pH modifier to the system. The pH of aqueousstream has significance primarily as a measure of the ph of the overallsystem. That is, when said effluent stream is at an acidic pH, thecontinuous overall system will likewise be at agenerally equivalent pH,including the waste water stream removed from the fabrictation zone, thesludge separated therefrom, the aqueous suspension in the milling zone,and, of course, the sheet being fabricated. The sheet applications otherthan roofing felt and similar applications, in which the sheet issubsequently to be contacted with hot, fluid organic materials, thefabrication of such an acid sheet is generally satisfactory from aproduct viewpoint.

In roofing felt production, the fabrication of an acid sheet appearssatisfactory insofar as the apparent properties of the constructionpaper sheet leaving the fabrication zone are concerned. Thus, the paperhas good absorption characteristics, good strength and good flexibilityand other desirable characteristics. Upon contact with hot asphalt inthe saturators in which the sheet is saturated therewith in theproduction of a finished roofing felt product, the solubilizingproperites of the hot asphalt are found to so weaken or otherwise alterthe roofing felt sheet that said sheet has a tendency to readily tear tothe extent that satisfactory passage through the saturators can not beeffectively maintained. In such applications, therefore, the system ismaintained under generally neutral conditions, the pH of the overallsystem being conveniently reflected by pH of the effluent aqueous streamrecycled to the milling zone as indicated above. The pH of the system iscommonly and advantageously controlled by the addition of caustic to thesystem, although other less desirable materials, such as lime, can alsobe employed for the desired pH control. While the pH of the effluentaqueous stream is a convenient measure of the pH of the system, thecaustic or other pH control modifier need not be added to the effluentaqueous stream itself, but may be added at any other convenient point ina particular effluent system as will readily be appreciated by thoseskilled in the art. It will also be appreciated that the pH of thesystem can be monitored at any other convenient point, as by monitoringthe pH of the vat fibers entering the fabrication zone. In roofing feltand other applications in which the fabricated sheet is contacted by hotorganic material, such as asphalt, having solubilizing properties withrespect to constituents of the sheet, the pH of the system, as reflectedby the pH of the effluent aqueous stream, is generally maintained withinthe range of from about 5.4 to about 6.5, preferably at from about 5.8to about 6.2, more preferably at about 5.9 to about 6.0. At lower pHvalues, the acid sheet will, as indicated, lack the requisite strengthfor acceptable passage through the necessary asphalt saturation zone inthe production of roofing felts. At higher pH values, as on the order ofabout 8.5, the sheet will be found to become brittle and generallyunsatisfactory. Before reaching this undesired point, however, thesystem will be subjected to highly disadvantageous foaming underalkaline conditions such as a pH of on the order of about 7.5 or less.For this reason, pH modification to avoid the production of an acidsheet advantageously is accomplished in a manner as to avoid thedifficulties thus associated with alkaline conditions to the degreereferred to above.

The effluent aqueous stream, having dissolved wood sugars, cresols,lignins and organic acids therein, but a substantial portion of thecolloidal material removed therefrom as sludge, is recycled to themilling zone as make-up water in a relatively warm condition. Theoverall heat requirements of the sheet fabrication operation are therebyreduced and minimized in the practice of the invention vis-a-visconventional operations in which fresh water must be preheated fromambient conditions to the desired temperature conditions under which theaqueous suspension is prepared and the sheet is fabricated. The recycleaqueous stream of the invention will have a temperature of from about100F to about 140F, commonly on the order of about 120F to about 125F.As compared with the necessity for heating fresh water from about 60F upto the operable temperature conditions for sheet fabrication, e.g.,about l35-l40F, the use of the relatively warm recycle effluent streamas herein provided results in an additional highly desirable feature ofthe present invention, not only from a technical and economic viewpointbut from an environmental aspect as well. Thus, localized energyshortages, and the prospects of curtailed operating schedules as aresult thereof, have occasioned genuine concern in various pulp andpaper facilities. The present invention not only makes a majorcontribution in the field of pollution control, therefore, but likewiseenables the desired sheet fabrication operations to be carried out withsignificantly reduced heat requirements and consequent demands for fuel.

In conventional operations, the sludge of colloidal material separatedfrom the effluent aqueous stream, typically at a consistency of about12l8% solids by weight, must be stored, transported and dischargedtoappropriate waste collection areas, all of which entails a veryconsiderable peripheral expense in the overall sheet fabricationOperations. Recycling said sludge to the milling zone for incorporationin the aqueous suspension of fibrous and non-fibrous materials treatedin the production of the sheet, as indicated above, disrupts theorientation of the fibers, resulting in poor fiber formation and alumpy, non-uniform sheet having inadequate strength and drainagecharacteristics, and

otherwise disrupts conventional operations and the quality of theproducts obtained. In the present invention, however, the sludge isneither discarded to waste nor utilized in such a disruptive andunsatisfactory manner. Rather the sludge is mixed with groundwood stockor other wood fiber prepared in conventional defibrators so as to coatthe sludge onto the individual strands of fiber. The wood fibers thuscoated with the accumulated sludge are passed to the milling zone as awood stock component of the aqueous suspension produced therein, paperstock and rag stock being blended therein in accordance with the desiredspecifications pertaining to any particular grade and type ofconstruction paper sheet. When recycled in this fashion, the sludge doesnot interfere with the customary interlocking and orientation of thefibers and does not have any appreciable adverse effect on theuniformity and properties of the resulting sheet. The sludge thusincorporated in the sheet likewise does not interfere with the.

customary drainage characteristics of the sheet or otherwise disruptconventional sheet fabrication operations. The resulting sheet producedin a closed cycle operation under essentially zero effluent dischargeconditions, therefore, has properties comparable to those ofconventional sheets produced without the recycle and incorporation ofsaid sludge therein.

As previously indicated, the wood stock component of the furnish fromwhich construction grade paper sheets are fabricated will generallycomprise groundwood stock, typically blended with paper stock and/or ragstock. The wood stock component will generally constitute at least onthe order of about one-third of the fibrous content of the furnish on adry fiber weight basis and, of course, correspondingly higher as thepaper stock and rag stock components may be reduced from the typicalamounts recited above in particular applications of the invention. Inall such construction paper applications, the wood fiber content of thefurnish will be sufficient in quantity to provide adequate fibers forthe coating of recovered sludge thereon for recycle in continuous sheetfabrication operations at essentially zero effluent discharge. It isalso within the scope of the invention to mix the accumulated sludgewith only a portion of the wood fiber content of the furnish, theremainder of said wood fiber being passed directly to the milling zonewithout precoating by said sludge.

To the extent that any of the sludge coated on the strands of wood fiberbecome dislodged and thereby present in fabricated sheet as looseparticles, it will be appreciated that the presence of such loose sludgeparticles in the fabricated sheet could tend to diminish somewhat theextent of the advantages of the sheet of the invention over sheetsproduced by the incorporation of the sludge therein as loose particles.To minimize any such tendency, therefore, a polyelectrolyte material isincorporated in the blend of wood fiber and sludge, in preferredembodiments of the invention, to enhance the adherence of the sludge onthe individual strands of fiber. The polyelectrolyte, which serves ineffect to bond the sludge to the fibers so as to minimize the amount ofsaid sludge dislodged therefrom upon subsequent recycle to the millingzone and the sheet fabrication zone, may conveniently be the same highmolecular weight, cationic polyelectolyte materials disclosed above foruse in the flocculation of clay particles having colloidal materialadsorbed thereon. The polyelectrolytes will ordinarily be employed as aslurry in fresh water as also noted above.

It will be appreciated that the amount of said polyelectrolyte materialemployed for bonding the sludge to the individual strands of wood fiberwill depend upon a variety of factors in any given application, e.g.,the nature of the wood fiber and sludge, the relative amounts thereof,the particular high molecular weight, cationic polyelectrolyte or othersaid polyelectrolyte bonding agent employed and the like. In general,however, the polyelectrolyte will commonly be employed in an amountwithin the range of from about to about 50% by weight of that employedfor flocculation pur' poses, typically on the order of about to aboute.g., 25% by weight thereof. Thus, the polyelectolyte bonding agent,such as the cationic polyacrylamide bonding agents referred to above,will ordinarily be employed in concentrations of on the order of 0.5 toabout 100 ppm, i.e., parts per million parts of said sludge-fiber slurryby weight, preferably about 1 to about 75 ppm, although it will beappreciated that amounts outside said ranges may be employed within thescope of the novel process of the invention.

Groundwood fibers having a somewhat gray appearance due to the presenceof sludge on the individual strands thereof, due to the blending ofsludge and fiber so as to coat, bond or otherwise adhere said recyclesludge to the fibers, may be blended in the milling zone with othercomponents of the furnish and employed in the fabrication zone withoutadverse effect on the formation of the sheet or its properties andcharacteristics.

In this regard, the sludge-coated fibers perform as conventionalnon-sludge-coated groundwood fiber performs, resulting in uniform,non-lumpy sheets, having good drainage characteristics and suitablestrength, said sheets being readily employed in roofing feltapplications without the tearing and breaking of the sheet uponapplication of hot asphalt as encountered heretofore in efforts torecycle sludge directly to the milling zone for incorporation in thefabricated sheet.

In particular illustrative embodiments of the invention, groundwoodfibers, such as pine and oak, are employed together with paper stock andrag stock in roofing felt production, with about one-third of thefibrous content of the furnish comprising groundwood fiber on a dryfiber weight basis. The dirty white water separated from the fabricatedsheet at about l40F has particulate objects and suspended fibers removedtherefrom, the resulting effluent aqueous stream being divided so thatabout 80% by weight thereof passes to the hydrapulpers employed in theproduction of said groundwood fiber. Upon having additional suspendedfiber material removed therefrom, the remaining portion of the effluentaqueous stream, i.e., about 20% of the clean white water stream,comprises a high BOD stream, e.g., about 2,000 BOD, at a temperature ofabout 1l5-l20F. In conventional, non-closed operations, the stream islikewise at a high BOD level, usually about 2,000 BOD. The subjectstream is contacted with a 2% by weight clay slurry in fresh water, saidclay comprising KWK Volclay bentonite clay employed in an amount ofabout 200 ppm based on the weight of said aqueous stream being treated.After about 2-3 minutes, the resulting clay slurry having adsorbedcolloidal material associated therewith is contacted with a very highmolecular weight polyacrylamide cationic flocculent, i.e., Magnifloc560-C flocculent, in an amount of about 7- /2 ppm based on the dryweight of said clay particles, thus facilitating the separation of theclayadsorbed colloidal material from the effluent aqueous stream aswaste sludge material. The effluent aqueous stream having its colloidalmaterial content thus significantly reduced is recycled to the millingzone at a pH of about 6.0. The recycle stream, having approximately 2.2%dissolved solids therein, is at a temperature of about F, minimizing theheat requirements to bring the contents of the milling zone up to thedesired temperature range, the sheet being fabricated at about -140F.The sludge separated from the effluent aqueous stream at about 120F at aconsistency of about 12% by weight in aqueous slurry is blended with thegroundwood fiber portion of the furnish so as to coat the individualfiber strands with the sludge. Using about 25% by weight of the amountemployed above for flocculation purposes, the indicated high molecularweight polyacrylamide, cationic flocculent is blended with the aqueousslurry of groundwood fiber with sludge coated thereon in order toenhance the bonding of the sludge to the individual fiber strands. Thesludge thus adhering to the fibers comprises essentially all of thewaste sludge, so that together with the indicated recycle of theeffluent aqueous stream, the overall sheet fabrication operation iscarried on on a closed-cycled basis with essentially zero effluentdischarge to waste.

The sludge, as thus bonded to the groundwood fiber, is recycled to themilling zone wherein said groundwood fiber, paper stock and rag stock,together with conventional non-fibrous ingredients, are blended andpassed to the fabrication zone. Therein, the sheet having said sludgeincorporated therein not as loose particles, but essentially adhering tothe groundwood fiber strands, is produced as a uniform, non-lumpy sheet.The sludge in this form does not interfere with the customeryorientation of the fibers to produce an acceptable sheet. As the systemlikewise was maintained at a pH of about 6 by the addition of causticthereto, the sheet thus-containing said waste sludge is suitable forroofing felt application and is found to readily pass throughconventional saturators without breaking upon exposure to hot asphalt.The resulting roofing felt, therefore, is comparable in quality withconventional roofing felt produced without recycle of said effluentaqueous stream and of said accumulated waste sludge.

It will be readily appreciated that various other conventionalingredients may be incorporated in the overall system herein describedto overcome or obviate particular operating difficulties or effectsencountered in such operations. Thus, a water soluble foam suppressant,such as Betz Foam-Trol C, a nonionic antifoam product designed for usein paper production may be employed in conventional amounts. Likewise,any suitable, commercially available corrosion-inhibiting agent can beincorporated in the system in conventional amounts as required. Atypical agent employed for this purpose is Betz Petromeen WS-54, asemipolar, water-soluble, organic filming agent. As the sludge materialshandled comprise biological waste material, it is also generallydesirable to employ a conventional slime-control agent, such asconventionally available chlorophenols such as Betz RX-l7, in the systemin conventionally recommended dosages. As with the other known agentsemployed for their customary purpose, such slime-control additives canbe employed at any convenient point in the overall system as describedherein. It will be appreciated, in this regard, that slime formation canoccur anywhere in the system and is not a problem peculiar to aclosed-cycle mill.

The dissolved solids present in the recyled effluent aqueous streamcomprise a variety of wood sugars, cresols, lignins and organic acids.In the continuous operations of the present invention, such solids inexcess of the saturation level of the aqueous streams involved in theoverall operation are present as suspended material that is removed fromthe effluent aqueous stream as sludge for incorporation in the sheet inaccordance with the essentially zero effluent discharge of the presentinvention. The sheet fabrication operation of the invention, in whichcomparable sheet quality is combined with total utilization of Wastematerials, represents a major contribution to the environmental aspectsof constuction paper fabrication. This contribution, most significantly,is made in a technically and economically feasible manner highly suitedfor commercial application. As extensive investigation has determinedthat the novel sheet produced with sludge incorporated therein, asherein provided, has acceptable properties and can successfully beemployed in roofing felt and like applications, it can be seen that,contraty to all expectations, essentially zero effluent dischargeoperations are, in fact, feasible, with the immense environmentaladvantages accruing to such operations.

Therefore, I claim:

1. An improved process for the production of constuction paper sheetscomprising:

a. blending fibrous stocks including groundwood stock having dissolvedsolids therein, together with water, in a milling zone to produce anaqueous suspension of said stocks;

b. dewatering said suspension in a sheet fabrication zone as tofabricate said paper sheets;

c. removing particulate objects and suspended fiber from the waste waterstream removed from said fabrication zone, thereby producing an effluentaqueous stream having dissolved and colloidal material present therein,said stream having a relatively high BOD loading;

d. separating said colloidal material from the effluent aqueous streamas a sludge of waste solids material;

e. blending said sludge and groundwood stock so as to coat individualstrands of the wood fibers with said sludge;

f. recycling essentially all of said effluent aqueous stream havingdissolved solids therein to said milling zone as make-up water forblending with additional quantities of said fibrous stocks; and

g. recycling said sludge coated on the fibers of said groundwood stockto the milling zone, the sludgecoated wood fibers serving as said woodstock components of the aqueous suspension produced in the milling zone,essentially all of said sludge separated from the effluent aqueousstream thus being recycled to said milling zone,

whereby said sheet is produced essentially without discharge of high BODaqueous effluent to waste and without undesired sludge accumulation, thedisruption of the orientation of the fibers of the resulting sheet, withaccompanying adverse effect on the properties and quality of the sheet,occasioned by the incorporation of loose sludge particles in the aqueoussuspension being substantially obviated by the indicated coating of saidsludge on the individual strands of wood fiber prior to incorporationinto said aqueous suspension, the properties of the resulting sheet thusbeing comparable to those of said sheet produced without the recycle andincorporation of said sludge therein.

2. The process of claim 1 in which a water-dispersible bonding agent isblended with said sludge and groundwood stock so as to bond said sludgeto the individual wood fiber strands, thereby minimizing undesireddislodging of said sludge from the wood fiber during the formation ofsaid aqueous suspension and the fabrication of said sheet.

3. The process of claim 2 in which said bonding agent comprises a highmolecular weight cationic polyelectrolyte.

4. The process of claim 2 in which said pH of the effluent aqueousstream is from about 5.4 to about 6.5.

5. The process of claim 2 and including dispersing bentonitic clayparticles in said effluent aqueous stream having dissolved and colloidalmaterial present therein, said clay serving to adsorb the colloidalmaterial from the effluent stream, facilitating said separation ofcolloidal material from the effluent stream.

6. The process of claim 5 and including contacting said effluent stream,subsequent to said dispersing of clay particles therein for theadsorption of colloidal material, with a water-dispersible flocculent,thereby flocculating said clay particles having colloidal materialadsorbed thereon, and thus further facilitating said separation ofcolloidal material from said effluent aqueous stream.

7. The process of claim 5 in which the pH of said effluent aqueousstream is from about 5.8 to about 6.2.

8. The process of claim 1 in which said waste water removed from saidfabrication zone is relatively hot, said effluent aqueous streamrecycled to said milling zone as make-up water having a temperature offrom about F to about 140F, thereby reducing the overall heatrequirements of the sheet production operation.

9. The process of claim 8 in which said recycled effluent water is at atemperature of from about F to about F.

10. The process of claim 8 in which the pH of said effluent aqueousstream is from about 5.8 to about 6.2.

11. The process of claim 10 and including dispersing bentonitic clayparticles in said effluent aqueous stream having dissolved and colloidalmaterial present therein.

12. The process of claim 11 and including contacting said effluentstream, subsequent to said dispersing of clay particles therein foradsorption of colloidal material, with a water-dispersible flocculent,thereby flocculating said clay particles having colloidal materialadsorbed thereon, and thus further facilitating said separation ofcolloidal material from said effluent aqueous stream.

13. The process of claim 4 in which said sheet produced comprises asheet of roofing felt.

14. The process of claim 13 in which the pH of said effluent aqueousstream is from about 5.8 to about 6.2.

15. The process of claim 14 in which the pH of said stream is from about5.9 to about 6.0.

16. The process of claim 13 in which said bonding agent comprises a highmolecular weight cationic polyelectrolyte.

17. The process of claim 13 and including dispersing bentonitic clayparticles in said effluent aqueous stream having dissolved and colloidalmaterial present therein,

said clay serving to adsorb the colloidal material from the effluentstream, facilitating said separation of colloidal material from saideffluent stream.

18. The process of claim 17 and including contacting said effluentstream, subsequent to said dispersing of clay particles therein for theadsorption of colloidal material, with a water-dispersible flocculent,thereby flocculating said clay particles having colloidal materialadsorbed therein and thus further facilitating said separation ofcolloidal material from the effluent aqueous stream.

19. The process of claim 18 in which said waste water removed from thefabrication zone is relatively hot, said effluent aqueous streamrecycled to said milling zone as make-up water having a temperature offrom about 100F to about 140F, thereby reducing the overall heatrequirements of the sheet production operation.

20. The process of claim 13 in which said roofing felt comprises a blendof said wood stock, paper stock, and rag stock.

21. The process of claim 20 and including recycling fiber removed fromthe waste water stream to said milling zone as paper stock.

22. The process of claim 20 in which the pH of said effluent aqueousstream is from about 5.9 to about 6.0.

23. The process of claim 5 in which the bonding agent is an organiccopolymer of acrylamide.

24. The process of claim 6 in which the bonding agent is an organiccopolymer of acrylamide and the flocculant is the same or a differentorganic copolymer of acrylamide.

25. The process of claim 23 in which the bonding agent is blended withsludge and groundwood stock in amounts between about 0.5 and about 100ppm based on total weight of said sludge and groundwood stock.

26. The process of claim 24 in which the flocculant is contacted withsaid effluent stream in amounts between about 7 and about 20 ppm basedon the total weight of said effluent stream.

1. AN IMPROVED PROCESS FOR THE PRODUCTION OF CONSTRUCTION PAPER SHEETSCOMPRISING: A. BLENDING FIBROUS STOCKS INCLUDING GROUNDWOOD STOCK HAVINGDISSOLVED SOLIDS THEREIN, TOGETHER WITH WATER, IN A MILLING ZONE TOPRODUCE AN AQUEOUS SUSPENSION OF SAID STOCKS; B. DEWATERING SAIDSUSPENSION IN A SHEET FABRICATION ZONE AS TO FABRICATE SAID PAPERSHEETS; C. REMOVING PARTICULATE OBJECTS AND SUSPENDED FIBER FROM THEWASTE WATER STREAM REMOVED FROM SAID FABRICATION ZONE, THEREBY PRODUCINGAN EFFLUENT AQUEOUS STREAM HAVING DISSOLVED AND COLLOIDAL MATERIALPRESENT THEREIN, SAID STREAM HAVING A RELATIVELY HIGH BOD LOADING; D.SEPARATING SAID COLLOIDAL MATERIAL FROM THE EFFLUENT AQUEOUS STREAM AS ASLUDGE OF WASTE SOLIDS MATERIAL; E. BLENDING SAID SLUDGE AND GROUNDWOODSTOCK SO AS TO COAT INDIVIDUAL STRANDS OF THE WOOD FIBERS WITH SAIDSLUDGE; F. RECYCLING ESSENTIALLY ALL OF SAID EFFLUENT AQUEOUS STREAMHAVING DISSOLVED SOLIDS THEREIN TO SAID MILLING ZONE AS MAKE-UP WATERFOR BLENDING WITH ADDITIONAL QUANTITIES OF SAID FIBROUS STOCKS; AND G.RECYCLING SAID SLUDGE COATED ON THE FIBERS OF SAID GROUNDWOOD STOCK TOTHE MILLING ZONE, THE SLUDGE-COATED WOOD FIBERS SERVING AS SAID WOODSTOCK COMPONENTS OF THE AQUEOUS SUSPENSION PRODUCED IN THE MILLING ZONE,ESSENTIALLY ALL OF SAID SLUDGE SEPARATED FROM THE EFFLUENT AQUEOUSSTREAM THUS BEING RECYCLED TO SAID MILLING ZONE, WHEREBY SAID SHEET ISPRODUCED ESSENTIALLY WITHOUT DISCHARGE OF HIGH BOD AQUEOUS EFFLUENT TOWASTE AND WITHOUT UNDESIRED SLUDGE ACCUMULATION, THE DISRUPTION OF THEORIENTATION OF THE FIBERS OF THE RESULTING SHEET, WITH ACCOMPANYINGADVERSE EFFECT ON THE PROPERTIES AND QUALITY OF THE SHEET, OCCASIONED BYTHE INCORPORATION OF LOOSE SLUDGE PARTICLES IN THE AQUEOUS SUSPENSIONBEING SUBSTANTIALLY OBVIATED BY THE INDICATED COATING OF SAID SLUDGE ONTHE INDIVIDUAL STRANDS OF WOOD FIBER PRIOR TO INCORPORATION INTO SAIDAQUEOUS SUSPENSION, THE PROPERTIES OF THE RESULTING SHEET THUS BEINGCOMPARABLE TO THOSE OF SAID SHEET PRODUCED WITHOUT THE RECYCLE ANDINCORPORATION OF SAID SLUDGE THEREIN.
 2. The process of claim 1 in whicha water-dispersible bonding agent is blended with said sludge andgroundwood stock so as to bond said sludge to the individual wood fiberstrands, thereby minimizing undesired dislodging of said sludge from thewood fiber during the formation of said aqueous suspension and thefabrication of said sheet.
 3. The process of claim 2 in which saidbonding agent comprises a high molecular weight cationicpolyelectrolyte.
 4. The process of claim 2 in which said pH of theeffluent aqueous stream is from about 5.4 to about 6.5.
 5. The processof claim 2 and including dispersing bentonitic clay particles in saideffluent aqueous stream having dissolved and colloidal material presenttherein, said clay serving to adsorb the colloidal material from theeffluent stream, facilitating said separation of colloidal material fromthe effluent stream.
 6. The process of claim 5 and including contactingsaid effluent stream, subsequent to said dispersing of clay particlestherein for the adsorption of colloidal material, with awater-dispersible flocculent, thereby flocculating said clay particleshaving colloidal material adsorbed thereon, and thus furtherfacilitating said separation of colloidal material from said effluentaqueous stream.
 7. The process of claim 5 in which the pH of saideffluent aqueous stream is from about 5.8 to about 6.2.
 8. The processof claim 1 in which said waste water removed from said fabrication zoneis relatively hot, said effluent aqueous stream recycled to said millingzone as make-up water having a temperature of from about 100*F to about140*F, thereby reducing the overall heat requirements of the sheetproduction operation.
 9. The process of claim 8 in which said recycledeffluent water is at a temperature of from about 120*F to about 125*F.10. The process of claim 8 in which the pH of said effluent aqueousstream is from about 5.8 to about 6.2.
 11. The process of claim 10 andincluding dispersing bentonitic clay particles in said effluent aqueousstream having dissolved and colloidal material present therein.
 12. Theprocess of claim 11 and including contacting said effluent stream,subsequent to said dispersing of clay particles therein for adsorptionof colloidal material, with a water-dispersible flocculent, therebyflocculating said clay particles having colloidal material adsorbedthereon, and thus further facilitating said separation of colloidalmaterial from said effluent aqueous stream.
 13. The process of claim 4in which said sheet produced comprises a sheet of roofing felt.
 14. Theprocess of claim 13 in which the pH of said effluent aqueous stream isfrom about 5.8 to about 6.2.
 15. The process of claim 14 in which the pHof said stream is from about 5.9 to about 6.0.
 16. The process of claim13 in which said bonding agent comprises a high molecular weightcationic polyelectrolyte.
 17. The process of claim 13 and includingdispersing bentonitic clay particles in said effluent aqueous streamhaving dissolved and colloidal material present therein, said clayserving to adsorb the colloidal material from the effluent stream,facilitating said separation of colloidal material from said effluentstream.
 18. The process of claim 17 and incLuding contacting saideffluent stream, subsequent to said dispersing of clay particles thereinfor the adsorption of colloidal material, with a water-dispersibleflocculent, thereby flocculating said clay particles having colloidalmaterial adsorbed therein and thus further facilitating said separationof colloidal material from the effluent aqueous stream.
 19. The processof claim 18 in which said waste water removed from the fabrication zoneis relatively hot, said effluent aqueous stream recycled to said millingzone as make-up water having a temperature of from about 100*F to about140*F, thereby reducing the overall heat requirements of the sheetproduction operation.
 20. The process of claim 13 in which said roofingfelt comprises a blend of said wood stock, paper stock, and rag stock.21. The process of claim 20 and including recycling fiber removed fromthe waste water stream to said milling zone as paper stock.
 22. Theprocess of claim 20 in which the pH of said effluent aqueous stream isfrom about 5.9 to about 6.0.
 23. The process of claim 5 in which thebonding agent is an organic copolymer of acrylamide.
 24. The process ofclaim 6 in which the bonding agent is an organic copolymer of acrylamideand the flocculant is the same or a different organic copolymer ofacrylamide.
 25. The process of claim 23 in which the bonding agent isblended with sludge and groundwood stock in amounts between about 0.5and about 100 ppm based on total weight of said sludge and groundwoodstock.
 26. The process of claim 24 in which the flocculant is contactedwith said effluent stream in amounts between about 7 and about 20 ppmbased on the total weight of said effluent stream.